To prolong the operating life of an electrode and to extend the range of operating currents within which stabilization of the electric arc and its space localization are provided, it is necessary that in the course of pretreatment of non-consumable electrodes according to a method disclosed in Swedish Pat. No. 397,765 formation of the work surface of the electrode is accomplished by conversion of the electrode material from a liquid phase to a solid one.
The formation of the work surface of the electrode is achieved only if two phases are simultaneously present thereon, that is a liquid and solid phase with conversion of the material of the active portion of the electrode from a liquid phase to a solid one.
Known to the prior art is a non-consumable electrode comprising a holder having a recess formed in the work end thereof, fixed in the holder is an active portion in contact with the bottom and side surface of the recess. The height of the active portion is lower than that of the recess wherein this active portion is fixed (Cf. U.S. Pat. No. 3,307,011).
This electrode has a narrow operating current range. An operating current range is a range from a minimum current I.sub.min to a maximum one I.sub.max which provides the following:
(1) stabilization of an arc and its spaced localization within the entire range of current control so that the operating current can be varied repeatedly in both ways, that is increased from I.sub.min to I.sub.max and decreased from I.sub.max to I.sub.min ;
(2) arc striking at any current value in the range from I.sub.min to I.sub.max inclusive;
(3) a low cathode voltage drop; and
(4) a low value of heat flow into the electrode.
The ratio between the lower limit of current to the upper limit thereof within the entire range of control is at best 1:5 for this electrode.
In the course of operation of this electrode the inner surface of the recess is destroyed because of arcing between the workpiece and the recess.
Besides, in the course of pretreatment of this electrode according to a method disclosed in Swedish Pat. No. 397,765 formation of the work surface of the active portion does not occur since the material of the active portion of the electrode is in a liquid phase.
Also known in the prior art is a non-consumable electrode for arc processes (Cf. U.S. Pat. No. 3,198,932), comprising a holder having a recess formed in the work end thereof. Fixed in the recess is an active portion flush with the surface of the work end of the holder, i.e. the height of the active portion is equal to that of the recess.
Since the height of the active portion in this electrode is equal to that of the recess, the inner surface of the recess is not destroyed in the course of operation of the electrode.
However, this electrode has a narrow range of current control within which arc stabilization is provided.
In the course of pretreatment of this electrode according to a method disclosed in Swedish Pat. No. 397,765 formation of the work surface of the active portion does not occur since the thermal state of the electrode does not provide conditions for the formation of a solid phase on the work surface of the electrode.
Also known in the prior art is a non-consumable electrode, primarily a cathode, for arc processes (Cf. U.S. Pat. No. 3,911,309) comprising a holder having a recess formed in the work end thereof, fixed in which is an active portion. The height of the active portion is greater than that of the recess, i.e. the work zone of the active portion extends beyond the holder.
In the course of pretreatment of this electrode according to a method disclosed in Swedish Pat. No. 397,765 formation of the work surface of the active portion is accomplished due to partial conversion of the material from a liquid phase to a solid one.
Insufficient formation of the work surface of the active portion of the electrode makes is impossible to extend the range of operating currents within which the stabilization of an electric arc and its space localization are provided.
Also known in the prior art is a non-consumable electrode for arc processes (Cf. U.S. Pat. No. 3,231,332) representing a rod holder with an active portion made as a core. The holder is made of tungsten, and the active portion is made of emission materials. It is possible to use various admixtures added to tungsten to improve its plasticity, but they do not affect the electron-emitting properties of the electrode. The active portion is made of electron-emission materials, such as thorium oxide, lanthanum oxide, and the oxides of other rare-earth materials, and has a lower operating performance than that of the outer layer.
This electrode operates in the range of currents not lower than 20A, the stabilization of an electric arc and its space localization being provided only with the increase of current intensity.
Besides, this electrode has rather narrow application potentialities due to the fact that the electric arc stabilization with current control in either direction is maintained within a very narrow range of currents, and the space instability of the electric arc makes it impossible to use such electrodes for welding of closely spaced ribs, edges, etc.
Furthermore, the space stability of the electric arc is disturbed after the expiration of time defined by the operating life of the electrode. The description the patent teaches that to restore the electrode, it should be sharpened. The upper portion of the electrode made of tungsten is removed until the active core of the electrode with a new reserve of emission materials is exposed. The electrode should be resharpened, which, requires special tools and, results in a substantial waste of scarce tungsten from which the holder is made.
This electrode is characterized by a high cathode voltage drop and cannot provide stable arc striking at low currents.